Adjustable curve ruler



April 1934. w. s. WESTON ADJUSTABLE CURVE RULER Filed July 16, 1931 5 Sheets-Sheet 1 April 3, 1934. w. s. WESTON ADJUSTABLE CURVE RULE'R Filed July 16, 1931 3 Sheets-Sheet 2 v Ira/elder" l l/f/h'am 5. Wesfon Filed July 16, 1951 3 Sheets-Sheet 3 Inventor William 5. Weston Patented Apr. 3, 1934 UNITED STATES PATENT oFFicE 4 Claims.

The invention relates to an adjustable ruler for the use of draftsmen and others when drawing or checking curves. It comprises a flexible arc member of constant length; rigid end members attached to the ends of the arc member and provided with edges or other means for indicating or defining lines that are tangent or radial to the arc member at the ends of the curvature thereof; and means pivotally connecting and arranged to hold the rigid end members, independent of the arc member, at the correct distance apart and the tangent or radial line-indicating means in correct relation to each other and the am member when the latter is flexed for any desired curve for which the instrument is designed to .be .used. My present invention is a modification of the curve ruler disclosed in my Patent No. 1,893,689, issued January 10, 1933;

; i a modification whereby the parts of the end members located on the convex side of the curve member, as shown in that application, are eliminated, and whereby .an instrument with the governing parts proportioned to provide either an arc of a spiral curve or.an arc of a circle may be used either .side up. The invention is hereinafter more fully described, illustrated in the accompanying drawings, and the novel features more particularly pointed out in the appended claims.

Referring to the drawings:

Figure 1,,is a plan view of the improved curve' ruler with the arc member in the straight line position.

.Figure 2 is aplan view of the instrument with the arc member flexed through an angle of 150 degrees and having the pivotal connections between the end members located and proportioned to provide a curve with the arc of curvature grade .ually decreasing from that of a short radius at "one end to that of a long radius at the other end; a curve commonly designated as a spiral.

Figure'3 is an elevation of Figure 2.

Figures 4 to 8, inclusive, are geometric illustrations used to describe the fundamental facts governing the construction and relation of the flexible arc member, the rigid end members, and the pivotal connections between the end members as embodied in the complete instrument of Figures 1, .2 and 3.

Figure 9 is an illustration of part of the lower end of Figure 2, showing more clearly the construction and relation-of the segmental gears.

Figure 10 is a geometric illustration similar to Figure .5, drawn toa larger scale, giving therelative dimensions and locations of fundamental points which may be utilized in the design and manufacture of the instrument, adjustable for arcs of spirals as described.

Figure 1.1 is a geometric illustration, similar to that of Figure 10, ,giving the relative dimensions and locations of fundamental points which may be used in the designand manufacture of the instrument, adjustable for arcs of circles.

The design of .my adjustable curve ruler is based on the fact that, in a curve ruler having a flexible curve member of constant length with rigid end members fixed at the ends thereof to provide tangent and radial .lines, there are a series of points infi-xed position relative to one end member, reach of which maybe paired with and held at constant distance from .a different point in a series of points which are :in fixed position relative .to the other end member when the flexible member is adjusted to any desired curvature, either that .of a circular arc -or of a spiral. In the patent mentioned, I utilized in the construction of the instrument two pairs of these fundamental points as actual pivot points for the-connections holding the endmembers incorrect relation for any desired curve. In the .construction of my improved instrument, I utilized only one pair of fundamental points in combination with aset of gears.

Referring now to the geometric .-illu s trations, the line vA represents the flexible member .of the instrument with its ends indicated by the letters PCand PT; these letters being-commonly used by engineers and .draftsmen to mark the two ends of a curve. At eachend, the lines T-andR represent edges carried .by :the rigid end members andheld tangent and radial to the-curve of the flexible member at :the ends PC and PT. In the following-description, the letters PC and PT are used in designating the end members. The flexiblemember A may be :made of spring steel of a uniform cross section andbf a highly resilient quality such that .it may --be curved from 'a straight line to a short radius curve without taking aper'manent set. In Figure 4, when the upper .PTend member is moved from the position with the flexible member .A "straight, as indicated by the .solidline, tonne of the positions with the-flexible'member curved, as indicated by the heavy dotted line, the relative angle and the distance between theiPC and PT members are such that the;strain developed in the curved flexible member "gradually decreases from .one end to the other. Since this strain is the result of the bending action, it will :be apparent that the radius of curvature is inversely proportional to the strain. When held to any one of the curved positions shown in Figure 4, the curvature is similar to and substantially that of a spiral with the radius gradually increasing from a short radius at the PT end to a long radius at the PC end.

That the curves illustrated in Figures 4 and 10 are those of spirals may be confirmed by a comparison of the angles between the tangents at the ends and the line of a chord drawn through the PC and PT; It is a well known fact that for an arc of a circle, the angles between the tangents at the ends and the chord are symmetrically the same. For a spiral covering, a

total angle anywhere up to 180 degrees, the ana total angle is reduced to that of the other spirals shown, the ratio of the chord angles is reduced. Theoretically, as the totalangle approaches zero, the angles at both ends also approach zero and the ratio approaches 1 to I.

F This change in the ratio is specifically illustrated in FigurelO. a

It will now be apparent that, for an instrument that is to be adjusted to give a curve covering a total angle anywhere up to 189 degrees,

-it is of vital importance that the angular relation and distance between the tangent members shall be under positive control. Figure 10 illustrates the same spirals shown in Figures 4 and 5. For these spirals, it is a fundamental fact that when the end member PT is moved in the -ber so controlled that the angle of movement of point 0 relative to point I when adjusting from the straight'line position tov any desired spiral is one-third the angle covered by the spiral. For example, angle p, Figure 5, for the shar est spiral, is equal to one-third the angle-covered by the spiral, which is the sum of angles m and n as shown for the same spiral in Figure 4. This ratio is specifically illustrated in Figure 10. For any one of the positions shown the sum of the a angles between the chord line and the tangent ble.

ends, representing the angle covered by the spiral, is equal to three times the angle through which the point 0 has moved relative to point I;

To connect points I'and 0 direct is impractica If the connection shouldbe made straight across the flexible member, the instrument. could not be used either side up. To meet this problem and hold the fundamental pointsI and O' at constant distance without connecting direct, I

.. have devised a'set of pivotal connections on the concave side of the flexible member arranged in parallelogram relation to points I and O and the theoretical line connecting them. The lines 5 of this construction are illustrated in Figures 6, '7 and'8. Figure 6 shows the relation in the straight line position, Figure 7 the relation for a spiral covering ninety degrees, and Figure 8 the relation for a spiral covering one hundred fifty degrees. On the PT end, inside the tangent line and in line with theoretical point O, I provide two pivot points 0 and O constituting one end of the parallelogram. A bar F pivoted to the fundamental point I on the PC end, and providing the other end of the parallelogram, carries pivot points I and I which are located the same distance respectively from point I that points 0 and O are from point 0. Bar G connecting pivot points I and O and bar H, the same length as bar G, connecting pivot points I and O are therefore parallel to each other and to the theoretical line connecting points I and 0. By means of this parallelogram, the distance between the fundamental points I and O is held constant for any adjustment like those of Figures '7 and 8.

The important detail of the intermeshing gear construction shown in Figures 1, 2 and 9 may now be described. While in Figure 8, the angular movement of the bar F governs and controls the angular movement of the PT end relative to the PC end, yet it will be apparent that the angular movement of the bars G and H relative to their straight line position must also be governed to insure the correct-movement of theoretical pivot 0 about pivot I for a spiral curve like those of Figures 4, 5 and 10. That is, the angle 1), Figure 8, must coordinate in a definite ratio with the angular movement or" bar F and the PT end. For the spirals as illustrated, in which line 1-0 moves only one degree to every three degrees that the PT end rotates, Iuse in combination with the bar F a set of intermeshing gears whereby, when the bar is moved on pivot I through a definite angle, rotating the PT end through the same angle, the bars G and H parallel to the line I-0 are caused to move angularly in the same direction only onethird that angle. For this purpose, the bar D riveted to the PC end member, 1 and 9, has a segment of a gear J like one side of a standard gear formed concentric to the pivot I. The parallel bar G at the end mounted in bar F also has a segment of a gear K like one side of a standard gear. Mounted in the bar F and intermeshing with the gear-segments J and K is an intermediate gear L. When the bar F is moved clockwise from the position of Figure 1 to that of Figure 2, the bar G, because of the gear L, is moved relatively in the opposite direction. For the construction illustrated, the radius of the gear J is two-thirdsthe radius of gear K.' As a result, when the bar F is moved clockwise through any angle, the bars G and H lag two thirds of that angle. For example, when the bar F is rotated one hundred fifty degrees in the adjustment from Figure l to Figure 2, the bars G and H are moved angularly only fifty degrees, bringing the PT end with tangent and radial lines in correct position. As already described in connection with Figure 4-, the bringing of PT end member to the desired adjustment, like in Figure 2, develops and holds a bending strain in the flexible member that causes it to take-the shape of the spiral.

I do not limit myself to the exact proportions of the parts as illustrated and thus far described. The proportions of the parts of the instrument illustrated in Figures 1 and 2 may be varied, using a pair of the fundamental pivot points in combination with three intermeshing gears which will hold the PC and PT end members for a spiral with a relatively much shorter radius at the short radius end. Also the parts may be proportioned to hold the PC and PT ends in the correct relation for an arc of a circle. Figure 11 illustrates the location of the points I and O and the proportion of the parts governing the construction of an instrument for drawing arcs of circles. For the proportions shown the ratio of the angle of movement of point 0 about point I to the angle covered by the arc, instead of being a constant value as chosen for Figure 10, changes gradually in the adjustment from the straight line position to that of an arc covering any angle up to 180. To provide for this change in the ratio, the segmental gears J and K and the intermeshing gear L will have their associated pivot points slightly eccentric to their true centers.

Referring now to the details of the construction of the instrument of Figures 1, 2 and 3. The flexible member A. which is illustrated by a double line, and is relatively thicker than in actual manufacture, is preferably attached to the end members by screws. Rivets are used for the rest or the connections, including the pivots for the rotating connections. The construction is similar to that or" a pocket knife with th rivets finished even with the surface. The end members are folded from sheet metal into a top and bottom plate with a space between as shown in Figure 3. At the PT end, the bars G and H extend into this space and are pivoted at points 0 and O shown. Within the PC end is riveted the arm D the pivot I and the segmental gear J. This space on the PC end provides clearance for gears K and L when in the position of Figures 2 and 9. The bar F is also folded from sheet metal and pivoted top and bottom over the segmental gear J. This end of the bar, both top and bottom, is rounded in eccentric shape so that it provides a contact with the concave side of the curve member near its long radius end. This detail is an advantage in holding this portion of the member, which is more pliable, against deflection by external pressure from a pen or pencil. In Figure 9 the top plate of the PC end member and the top fold of bar F is mostly cut off, as indicated by the irregular lines, to show clearly the relation of segmental gears and the intermediate Because of the strain developed in the flexible member, it is necessary to lock the angles of the connections and the parallelogram after the instrument has been adjusted to the desired curvature. For this purpose, I have mounted on bar G a sleeve V with points on one end that interlock with a saw-tocth edge of both top and bottom plates or" the PT end member, the saw tooth edge of the bottom plate being directly below and identical in every respect with that of the top plate. This sleeve is held to the interlock, after the adjustment has been made, by means or a spring S interposed between it and another sleeve W that is riveted in place on bar G.

The scale on the PT and member to which the arrow on the sleeve V points indicates the angle covered by the curve member. Its principal use is to enable the draftsman to more readily reset the instrument to any particular adjustment previously used. In the instrument as illustrated, the radial lines R of the end members are short, not being essential for most drafting purposes, and are used primarily to indicate the theoretical PC and PT ends of curvature of the curve member.

My present invention embodies the essential elements in the construction of an adjustable curve ruler, having means for holding it to any desired adjustment, that can be used either side up. Both sides are alike, the only difierence in the instrument illustrated in Figure 2 being that they provide for spirals in opposite directions. In the manufacture of the instrument, it may be made relatively thinner than shown in Figure 3.

I claim as my invention:

1. An adjustable curve ruler comprising a flexible curve member, rigid end members attached to the curve member and providing edges tangent and radial to said curve member at the ends of the curvature thereof, a set of bars pivotally connecting the end members whereby said end members may be moved and rotated relative to each other in the process of adjusting the curve of the flexible curve member, a set or" intermeshing gears governing the relative angular movements of said end members and said bars at their pivotal connections, and means for locking said angular movements at any desired angle of adjustment, and thereby holding the end members the correct distance apart for the adjustment.

2. In an adjustable curve ruler, the combination of a flexible curve member, a pair of end iembers respectively secured to said curve memher at its ends, and means for controlling the adjustment of end members relative to each other to thereby control the curvature of said curve member, comprising a bar pivoted to one of said end members, parallel bar means pivotally connecting said first-mentioned bar and the other or" said end members, and locking means independent or" said curve member for holding the bar and parallel bar means and said end members in fixed adjusted position relative to each other, whereby distortion of the curve member is adeouately resisted.

3. In an adjustable curve ruler, the combination or" a flexible curve member, a pair of end members respectively secured to said curve memher at its ends, and means for controlling the adjustment of said end members relative to each other to thereby control the curvature of said curve member, comprising a bar pivoted to one of said end members, parallel bar means pivotally connecting said first-mentioned bar and the other of said end members, and an intermeshing gear connection between said parallel bar means and the end member to which said first-mentioned bar is pivoted, said gear connection serving to control the relative movements of said end members and locking means acting through said gear connection to hold said end members rigidly in selected position of adjustment to thereby adequately resist distortion or said curve member from its normal curved position incident to the relationship of the end members.

l. An adjustable curve ruler comprising a flexble curve member, end plates rigidly attached to the ends of the curve member, a set of bars pivotally connected together and to the end plates, and interlocking means for controlling the relative movement of the end members and serving to maintain the same rigidly in selected position of adjustment to thereby adequately resist distortion of the curve member from its normal position incident to said selected position of adjustment.

WILLIAM S. WESTON. 

